Wireless communication device, wireless communication system, wireless communication method and program for randomizing a duration for receiving a probe request

ABSTRACT

Provided is a wireless communication device which includes a notification information transmitting unit for transmitting, via a wireless communication network, notification information of the wireless communication device, a notification information receiving unit for receiving notification information transmitted from another device, a frequency switching unit for successively switching, at random cycles, a frequency at which the notification information is transmitted or a frequency at which the notification information is received, and a transmission processing unit for performing a data transmission process after transmitting or receiving an acknowledgement to the notification information to/from such other device.

This is a continuation division of application Ser. No. 12/750,346,filed Mar. 30, 2012, which claims priority from Japanese PatentApplication JP 2009-094369 filed in the Japan Patent Office on Apr. 8,2009. The entire contents of the above-referenced applications areexpressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wireless communication device, awireless communication system, a wireless communication method, and aprogram.

Description of the Related Art

In recent years, due to advantages such as a greater degree of freedomof devices or the like, a wireless network typified by IEEE 802.11,which is a LAN standard, is becoming more popular, taking the place of awired network, and applications that are used are becoming more varied.

CITATION LIST Patent Literature

-   [Patent Literature 1] JP-A-2005-223767-   [Patent Literature 2] JP-A-2005-151525-   [Patent Literature 3] JP-A-2005-51522

SUMMARY OF THE INVENTION

In the infrastructure mode of IEEE 802.11, the operation of an accesspoint (AP) is started first, and notification information (beacon) isperiodically transmitted from the access point at a frequency that isset in advance. A station (STA) finds the access point, which is acommunication counterpart, by receiving the beacon transmitted from theaccess point.

On the other hand, a method is assumed of determining an access pointand a station by negotiation after connection has been completed,without distinguishing in advance an access point and a station amongcommunicating devices. According to this method, since it is not knownat what frequency the counterpart is operating, notifications, such asbeacons, are transmitted while switching the frequencies, and when thefrequencies of devices match at a certain timing, the notificationinformation can be received for the first time and connection can becompleted.

However, in this case, if frequency switching timing of a device matchesthat of a communication-counterpart device, a situation is assumed whereswitching progresses with the frequency of the devices remainingdifferent and notification information transmitted from a communicationcounterpart will not be received.

In light of the foregoing, it is desirable to provide a wirelesscommunication device, a wireless communication system, a wirelesscommunication method, and a program which are novel and improved, andwhich enable to reliably look for a communication counterpart whileswitching frequencies.

According to an embodiment of the present invention, there is provided awireless communication device which includes a notification informationtransmitting unit for transmitting, via a wireless communicationnetwork, notification information of the wireless communication device,a notification information receiving unit for receiving notificationinformation transmitted from another device, a frequency switching unitfor successively switching, at random cycles, a frequency at which thenotification information is transmitted or a frequency at which thenotification information is received, and a transmission processing unitfor performing a data transmission process after transmitting orreceiving an acknowledgement to the notification information to/fromsuch other device

Transmission of the notification information by the transmitting unitand waiting for receipt of the notification information by the receivingunit may be performed in time-division manner. There may be provided arandom period setting unit for setting a cycle for transmitting thenotification information or a waiting cycle for the receipt of thenotification information to a random period.

There may be provided an acknowledgement transmitting unit fortransmitting, in case the notification information transmitted fromanother device is received by the notification information receivingunit, the acknowledgment to such other device.

There may be provided a reception processing unit for receiving theacknowledgement to the notification information of the wirelesscommunication device from another device which has received thenotification information of the wireless communication device.

Transmission of the notification information by the transmitting unitmay be performed at a determined specific frequency.

Reception of the notification information by the receiving unit may beperformed at a determined specific frequency.

The transmitting unit may transmit a beacon as the notificationinformation, and the receiving unit may receive an acknowledgement tothe beacon transmitted as the notification information.

The transmitting unit may transmit a probe request as the notificationinformation, and the receiving unit may receive a probe response to theprobe request transmitted as the notification information.

According to another embodiment of the present invention, there isprovided a wireless communication system which includes a first wirelesscommunication device including a first notification informationtransmitting unit for transmitting, via a wireless communicationnetwork, notification information of the first wireless communicationdevice, a first notification information receiving unit for receivingnotification information transmitted from another device, a firstfrequency switching unit for successively switching, at random cycles, afrequency at which the notification information is transmitted or afrequency at which the notification information is received, and a firsttransmission processing unit for performing a data transmission processafter transmitting or receiving an acknowledgement to the notificationinformation to/from such other device, and a second wirelesscommunication device including a second notification informationtransmitting unit for transmitting, via the wireless communicationnetwork, notification information of the second wireless communicationdevice, a second notification information receiving unit for receivingnotification information transmitted from another device, a secondfrequency switching unit for successively switching, at random cycles, afrequency at which the notification information is transmitted or afrequency at which the notification information is received, and asecond transmission processing unit for performing a data transmissionprocess after transmitting or receiving an acknowledgement to thenotification information to/from such other device. The second wirelesscommunication device may receive the notification informationtransmitted from the first wireless communication device, transmit theacknowledgement to the first wireless communication device, and performthe data transmission process with the first wireless communicationdevice.

According to another embodiment of the present invention, there isprovided a wireless communication method which includes the steps oftransmitting, via a wireless communication network, notificationinformation of a wireless communication device, waiting for notificationinformation transmitted from another device, successively switching, atrandom cycles, a frequency at which the notification information istransmitted or a frequency at which the notification information isreceived, and performing a data transmission process after transmittingor receiving an acknowledgement to the notification information to/fromsuch other device.

According to another embodiment of the present invention, there isprovided a program for causing a computer to function as means fortransmitting, via a wireless communication network, notificationinformation of a wireless communication device, means for receivingnotification information transmitted from another device, means forsuccessively switching, at random cycles, a frequency at which thenotification information is transmitted or a frequency at which thenotification information is received, and means for performing a datatransmission process after transmitting or receiving an acknowledgementto the notification information to/from such other device.

According to the embodiments of the present invention described above,there can be provided a wireless communication device, a wirelesscommunication system, a wireless communication method, and a programwhich are novel and improved, and which enable to reliably look for acommunication counterpart while switching frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sequence diagram showing a flow of a sequence untilcommunication is started between an access point and a station, in theinfrastructure mode of IEEE 802.11;

FIG. 2 is a sequence diagram showing an example of transmittingnotification information by using a beacon in communication by directconnection;

FIG. 3 is a sequence diagram showing a case where frequency changecycles of a station 1 and a station 2 match;

FIG. 4 is a block diagram showing an example of the configuration of awireless communication device according to each embodiment of thepresent invention;

FIG. 5 is a schematic diagram showing a flow of a sequence according toa first embodiment; and

FIG. 6 is a schematic diagram showing a flow of a sequence according toa second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

The explanation will be given in the following order.

<1. First Embodiment>

(1) Technical Basis

(2) Communication Method where Access Point is Not Determined in Advanceand Its Demerit

(3) Configuration of Wireless Communication Device

(4) Flow of Processes according to First Embodiment

<2. Second Embodiment>

(1) Flow of Processes according to Second Embodiment

1. First Embodiment (1) Technical Basis

Most of the wireless LAN connection modes defined by IEEE 802.11, whichis a wireless LAN standard, are an infrastructure mode of performingcommunication via an access point. At the time of connecting wirelessly,a radio has to somehow find a connection counterpart. To find here meansto be in a state where synchronization of frequency channels and timingscan be established.

In the infrastructure mode of IEEE 802.11, the operation of an accesspoint (AP) is started first, and a beacon is periodically transmitted ata frequency (referred to as F1) that is set in advance. Here, the beaconis notification information including an ESS-ID, which is an identifierof a network, a time stamp, which is time information in the network, alist of supported wireless transmission rates, or the like. A station(STA) finds the access point (AP), which is a communication counterpart,by receiving the beacon transmitted front the access point. At thistime, the frequency of the station (STA) may be set by a user to be thesame as the frequency F1 of the access point (AP). Alternatively, thefrequency of the station (STA) may be set such that the stationcontinues reception while switching the frequency channels defined byIEEE 802.11 one by one until the station detects the beacon.

FIG. 1 is a sequence diagram showing a flow of a sequence untilcommunication is started between an access point and a station, in theinfrastructure mode of IEEE 802.11. First, the power of an access pointis turned on in step S10, and the access point starts transmission ofbeacon at the frequency F1 in the next step S12. Additionally, theaccess point can autonomously find the frequency set by a user or afrequency at which an access point is vacant. After the power is turnedon in step S20, the station starts waiting for a beacon in step S22. Thestation keeps waiting while switching frequencies.

In step S24, the frequency at which the station waits for a beacon isset to F1. Accordingly, a beacon (frequency F1) transmitted from theaccess point is received at the station, and in step S26, the stationperceives the existence of the access point.

Then, authentication and association are performed between the accesspoint and the station, and connection is completed in step S28. Afterthe connection is completed, a beacon is transmitted from the accesspoint to the station, and data communication between the access pointand the station is started.

(2) Communication Method where Access Point is not Determined in Advanceand its Demerit

On the other hand, a method can be assumed according to which twoterminals are connected by direct connection in a simple manner by usingthe mechanism of IEEE 802.11 wireless LAN without the user consciouslydistinguishing between an access point and a station. According to thismethod, the terminals are equal to each other without the distinction ofaccess point and station, and at the time of communication, both startsearching for each other at the same time. Negotiation is performedafter each other is found, and one plays the role of a simple accesspoint, and the other plays the role of a station. Accordingly, thismethod enables to realize a simple infrastructure mode withoutdistinguishing between an access point and a station.

According to the method described above, two terminals have to find eachother simultaneously without which terminal is to play the role ofstarting continuous transmission of beacons (the role of the accesspoint) being determined. At this time, the two terminals start operationwhile still not knowing the frequency of a counterpart and not evenknowing if a counterpart exists at all. Accordingly, the two terminalshave to transmit notification information while switching thefrequencies, and at the same time, to wait in anticipation of receptionof notification information of a counterpart.

FIG. 2 is a sequence diagram showing an example of transmittingnotification information by using a beacon in communication by directconnection using the mechanism of IEEE 802.11 wireless LAN. First, thepower of a station 1 (STA1) is turned on in step S30. In the next stepS32, the station 1 transmits a beacon at the frequency F1, and aftertransmitting the beacon, waits, in step S34, for a response from otherstation at the frequency F1.

On the other hand, at a station 2 (STA2), power is turned on in stepS40. In the next step S42, the station 2 transmits a beacon at thefrequency F1, and after transmitting the beacon, waits, in step S44, fora response from other station at the frequency F1.

In the example of FIG. 2, the frequency F1 of the beacon transmitted bythe station 1 and the frequency F1 at which the station 2 is waitingmatch. Accordingly, the station 2 can receive the beacon transmitted bythe station 1. When receiving the beacon transmitted by the station 1,the station 2 perceives the existence of the station 1 in step S46.Then, negotiation for determining which is to play the role of an accesspoint is performed between the station 1 and the station 2. As a resultof a the negotiation, it is determined in step S48 that the station 1will play the role of an access point, and the connection is completed.In this case, the station 2 will play the role of a station (station(STA) shown in FIG. 1) in the infrastructure mode. After the connectionis completed, a beacon is transmitted from the access point to thestation, and data communication is performed between the access pointand the station.

As described above, according to communication by direct connectionusing the mechanism of IEEE 802.11 wireless LAN, a simple infrastructuremode can be realized by negotiation at the time of connection, withoutdetermining in advance which device is to play the role of an accesspoint or a station.

However, according to the communication by direct connection describedabove, notification information (beacons) are continuously transmittedwith the frequencies continuously changing. Thus, if the frequencychange cycles of the station 1 and the station 2 match, the frequenciesare changed while maintaining the state where the frequencies areshifted from each other, and the terminals may not find each other. FIG.3 is a sequence diagram showing a case where frequency change cycles ofthe station 1 and the station 2 match.

First, when the power of the station 1 (STA1) is turned on in step S50,the station 1 sets a communication frequency to F1 in the next step S52.In the next step S54, the station 1 transmits a beacon at the frequencyF1, and after transmitting the beacon, waits, in step S56, for aresponse from other station at the frequency F1.

On the other hand, when the power of the station 2 (STA2) is turned onin step S60, the station 2 sets a communication frequency to F2 in thenext step S62. In the next step S64, the station 2 transmits a beacon atthe frequency F2, and after transmitting the beacon, waits, in step S66,for a response from other station at the frequency F2.

The station 1 switches the frequency to F2 in step S58, and transmits abeacon and waits as in steps S54 to S56. Subsequently, the station 1periodically switches the frequency in the order of F3→F1→+F2→F3, andperforms the same processes.

The station 2 also switches the frequency to F3 in step S68, andtransmits a beacon and waits as in steps S64 to S66. Subsequently, thestation 2 periodically switches the frequency in the order ofF1→F2→F3→F1, and performs the same processes.

In FIG. 3, when the station 1 transmits a beacon at the frequency F1(step S54) and is waiting at the frequency F1 (S56), the station 2transmits a beacon at the frequency F2 (step S64) and is waiting at thefrequency F2 (step S66). Therefore, neither the station 1 nor thestation 2 can perceive the other because their respective frequenciesare different. Also, in FIG. 3, the frequency switching cycle is thesame for the station 1 and the station 2. Thus, even if each of thestations 1 and 2 switches the frequency after step S58 or S68, thefrequency at which the station 1 performs transmission and the frequencyat which the station 2 is waiting will not match. Also, the frequency atwhich the station 2 performs transmission and the frequency at which thestation 1 is waiting will not match. Therefore, both station 1 andstation 2 will not perceive each other.

(3) Configuration of Wireless Communication Device

FIG. 4 is a block diagram showing an example of the configuration of awireless communication device 100 according to each embodiment of thepresent invention. The wireless communication device 100 is configuredto be able to communicate with other wireless communication device by awireless communication network such as IEEE 802.11a, IEEE 802.11h andIEEE 802.11n, which are wireless LAN standards. As shown in FIG. 1, eachwireless communication device 100 includes a data processing unit 102, atransmission processing unit 104, a wireless interface unit 106, acontrol unit 108, a memory 110, and an antenna 112.

At the time of transmission, the data processing unit 102 createsvarious data frames and data packets in response to a request from anupper layer, for example, and supplies the same to the transmissionprocessing unit 104. The transmission processing unit 104 performs, atthe time of transmission, processing such as adding to a packetgenerated at the data processing unit 102 various data heads or an errordetection code such as a frame check sequence (FCS), and provides thedata which has been processed to the wireless interface unit 106. Thewireless interface unit 106 generates, from the data received from thetransmission processing unit 104, a modulation signal in a frequencyband of a carrier, and makes the same transmitted from the antenna 112as a radio signal.

Furthermore, at the time of performing a reception operation, thewireless interface unit 106 decodes the various data frames bydown-converting the radio signal received by the antenna 112 andchanging the same to a bit sequence. That is, the wireless interfaceunit 106 can function, in cooperation with the antenna 112, as atransmitting unit and a receiving unit. The transmission processing unit104 analyzes the headers added to the various data frames supplied fromthe wireless interface unit 106 and checks, based on the error detectioncode, that each data frame includes no error, and then, supplies thevarious data frames to the data processing unit 102. The data processingunit 102 processes and analyzes the various data frames and data packetssupplied from the transmission processing unit 104.

The control unit 108 is a block for controlling the respectiveoperations of the data processing unit 102, the transmission processingunit 104, and the wireless interface unit 106. The control unit 108performs operations such as determination of a transmission/receptionfrequency, creation of a control message (notification information suchas a beacon, a beacon acknowledgement, a probe request and a proberesponse), issuance of a transmission command for the control message,and interpretation of the control message. Also, the control unit 108controls various operations of the wireless communication device 100,such as reception operation and transmission operation.

As shown in FIG. 4, the control unit 108 includes, as main structuralelements, a notification-information creation/transmission-instructionunit 108 a, a reception/interpretation processing unit 108 b, afrequency switching unit 108 c, and a random period setting unit 108 d.The notification-information creation/transmission-instruction unit 108a creates the control message, or issues a transmission command for thecontrol message. The reception/interpretation processing unit 108 bperforms a reception process or an interpretation process for thecontrol message transmitted from the communication counterpart. Thefrequency switching unit 108 c performs an operation of switchingtransmission frequencies or of switching waiting frequencies. The randomperiod setting unit 108 d performs an operation of setting atransmission cycle or a waiting cycle to a random period.

The memory 110 plays the role of a work area for the data processing bythe control unit 108, and has a function of a storage medium for holdingvarious types of data. Various storage media, for example, a volatilememory such as a DRAM, a non-volatile memory such as an EEPROM, a harddisk and an optical disk, may be used as the memory 110. Additionally,each block shown in FIG. 4 can be configured from hardware (circuit).Furthermore, each block can be configured from a processor (CPU) andsoftware (program) for making the processor function. In this case, theprogram can be stored in the storage medium included in the wirelesscommunication device 100, such as the memory 110.

(4) Flow of Processes According to First Embodiment

The present embodiment makes the frequency change cycle inconstant(random) in view of the issue described with FIG. 3. FIG. 5 is aschematic diagram showing a flow of a sequence according to the presentembodiment. As with FIG. 3, two stations (STA1 and STA2) are to look fora communication counterpart. Both stations 1 and 2 are assumed to have afunction conforming to IEEE 802.11. Also, as with FIG. 3, usablefrequencies are F1, F2 and F3 for both stations 1 and 2.

There are two kinds of messages to be transmitted by each of the station1 and the station 2, namely, a beacon and a beacon acknowledgement whichis transmitted at the time of receiving a beacon. Also, there are fourstates in relation to the states of each of the station 1 and thestation 2, namely, beacon transmission, waiting, frequency changing, andbeacon response transmission.

In FIG. 5, the station 1 is to transmit a beacon at the frequency F1during the beacon transmission cycle. Also, the station 2 is to transmita beacon at the frequency F2. With both station 1 and station 2, thetransmission of a beacon is to be alternately performed every 2 cyclesof the frequency switching cycles and waiting is to be performed everycycle.

First, when the power of the station 1 (STA1) is turned on in step S100,the station 1 sets a communication frequency to F1 in the next stepS102. In the next step S104, the station 1 transmits a beacon at thefrequency F1, and after transmitting the beacon, waits, in step S106,for a response from other station at the frequency F1.

On the other hand, at the station 2 (STA2), when the power is turned onin step S200, a communication frequency is set to F2 in the next stepS202. In the next step S204, the station 2 transmits a beacon at thefrequency F2, and after transmitting the beacon, waits, in step S206,for a response from other station at the frequency F2.

Then, in step S208, the station 2 sets the frequency to F3. Since thetransmission of a beacon is performed every 2 cycles of the frequencyswitching cycles, the station 2 waits without transmitting a beacon atthe frequency F3 (step S210). Then, the frequency is switched to F2 instep S212, and a beacon is transmitted at the frequency F2 in the nextstep S214.

The station 1 changes the frequency to F2 in step S108. Since, also atthe station 1, the transmission of a beacon is performed every 2 cyclesof the frequency switching cycles, the station 1 waits withouttransmitting a beacon at the frequency F2 (S110). Thus, the transmissiontiming of a beacon (frequency F2) by the station 2 in step S214 isduring the time the station has started to wait (frequency F2) in stepS110 and is still waiting at the frequency F2. This is because, in thiscase, steps S212 and S214 of the station 2 occurred before the timing ofthe station 1 changing the frequency after step S108, because the cycleof the station 1 for changing the frequency after step S108 was set tobe random. Therefore, the station 1 receives the beacon transmitted fromthe station 2 at the frequency F2, perceives the existence of thestation 2 in step S112, and transmits a beacon response in the next stepS114.

The station 2 receives the beacon response transmitted from the station1 and perceives the existence of the station 1 in step S216. Then,negotiation is performed between the station 1 and the station 2 todetermine which is to play the role of an access point. Here, it isassumed that, as a result of the negotiation, the station 1 isdetermined to play the role of an access point in the infrastructuremode (step S218), and the connection is completed. In this case, thestation 2 will play the role of a station in the infrastructure mode.After the connection is completed, data communication is performedbetween the station 1 and the station 2.

In the sequence of the present embodiment shown in FIG. 5, the cycle fortransmitting beacons, the cycle for waiting, or the cycle for changingthe frequencies is set to a random period for each of the stations 1 and2. Referring to the station 2 as an example, a time T1 from a timing ofstarting the waiting at the frequency F3 (step S210) to a timing ofchanging to the frequency F2 (step S212) can be set as the randomperiod. Also, a time T2 from a timing of setting to the frequency F3(step S208) to a timing of changing to the next frequency F2 (step S212)can be set as the random period.

Also, in case of the cycle for waiting after the transmission of abeacon, a time 13 from a timing of transmitting a beacon at thefrequency F2 and of starting to wait (step S206) to a timing of changingto the next frequency F3 (step S208) can be set as the random period.

Also, a time T4 from setting the transmission frequency for a beacon toF2 (step S202) to a timing of changing to the next frequency F3 (stepS208) can be set as the random period.

Also, a portion equivalent to 2 cycles of the frequency switching cyclesmay be set as the random period. For example, a time 15 from setting thetransmission frequency for a beacon to F2 (step S202) to a next timingof setting the transmission frequency for a beacon to F2 (step S212) maybe set as the random period.

In this manner, by setting the cycle for transmitting beacons, the cyclefor waiting, or the cycle for changing the frequencies at a randomperiod, frequencies can be prevented from being switched, at the samecycles at both station 1 and station 2. Accordingly, a state asdescribed with FIG. 3 in which the terminals will not find each othercan be reliably prevented.

The random period may be period generated by a random number generator,for example. By ending a waiting state at a certain frequency at atiming of elapse of a random period and switching to the next frequency,a situation as described in FIG. 3 where devices will not find eachother can be reliably prevented.

Additionally, in FIG. 5, it is assumed that the transmission of a beaconis performed every 2 cycles of the frequency switching cycles at each ofthe stations 1 and 2. However, as with FIG. 3, the transmission of abeacon and waiting can be performed every cycle. In this case, thetransmission frequency for a beacon can also be changed every cycle aswith FIG. 3.

Additionally, although beacons are transmitted at a constant frequencyat all times in FIG. 5, the beacons may be transmitted at periodicallydifferent frequencies (for example, F1→F2→F3→F1, . . . ).

2. Second Embodiment (1) Flow of Processes According to SecondEmbodiment

Next, the second embodiment of the present invention will be described.The configuration of a wireless communication device 100 according tothe second embodiment is the same as that of the first embodimentdescribed with FIG. 4. The waiting time for receiving a beacon was maderandom in the first embodiment. However, in the second embodiment, acycle for transmission or a cycle for waiting is set to a random periodin case of receiving a probe response as a response to a probe request.The probe request here is notification information including anidentifier of a network, supported communication rate information,identification information of each station, or the like.

In the second embodiment, there are two kinds of messages to betransmitted by each of the station 1 and the station 2, namely, a proberequest and a probe response. Also, there are four states in relation tothe states of each of the station 1 and the station 2, namely, proberequest transmission, waiting, frequency changing, and probe responsetransmission.

FIG. 6 is a schematic diagram showing the flow of processes. It isassumed that, for both the station 1 and the station 2, the transmissionof a probe request is performed every 2 cycles of the frequencyswitching cycles and waiting is performed every cycle.

First, when the power of a station 1 (STA1) is turned on in step S300,the station 1 sets a communication frequency to F1 in the next stepS302. In the next step S304, the station 1 transmits a probe request atthe frequency F1. Then, after transmitting the probe request, thestation 1 waits, in step S306, for the reception of a probe response tothe probe request that has been transmitted.

On the other hand, when the power of a station 2 (STA2) is turned on instep S400, a communication frequency is set to F3 in the next step S402.The station 2 transmits a probe request at a frequency F2 in the nextstep S404. Then, after transmitting the probe request, the station 2waits, in step S406, for a probe response to the probe request that hasbeen transmitted.

Then, in step S408, the station 2 sets the frequency to F1, and waitsfor a probe request at the frequency F1 in step S410. Then, in stepS412, the frequency is switched to F3, and a probe request istransmitted at the frequency F3 in the next step S414.

The station 1 changes the frequency to F3 in step S308, starts waitingfor a probe request at the frequency F3 in the next step S310, and willkeep waiting. Then, the transmission timing of a probe request(frequency F3) by the station 2 in step S414 matches the timing of thestation 1 waiting (frequency F3), after step S310, for a probe request.This is because, in this case, steps S412 and S414 of the station 2occurred before the timing of the station 1 changing the frequency afterstep S308, because the cycle of the station 1 for changing the frequencyafter step S308 was set to be random. Therefore, the station 1 receivesthe probe request transmitted from the station 2 at the frequency F3,perceives the existence of the station 2 in step S312, and transmits aprobe response in the next step S314.

The station 2 receives the probe response transmitted from the station 1and perceives the existence of the station 1 in step S416. Then,negotiation is performed between the station 1 and the station 2 todetermine which is to play the role of an access point. Here, it isassumed that, as a result of the negotiation, the station 1 isdetermined to play the role of an access point in the infrastructuremode (step S418), and the connection is completed. In this case, thestation 2 will play the role of a station in the infrastructure mode.After the connection is completed, data communication is performedbetween the station 1 and the station 2.

Also in the sequence of the embodiment shown in FIG. 6, the waiting timeis set to a random period for both station 1 and station 2. Referring tothe station 2 as an example, any of T6 to T11 shown in FIG. 6 or some ofT6 to T11 can be made to be the random period.

In the present embodiment, in case of transmitting a probe request, itis assumed for both station 1 and station 2 that the probe request istransmitted with usable frequencies periodically switched in turn. InFIG. 6, the station 1 switches the frequency in the order such asF1→F2→F3→F1 . . . , and the station 2 switches the frequency in theorder such as F2→F3→F1→F2 . . . .

On the other hand, since the counterpart is transmitting probe requestswhile switching the frequencies, a probe request is to be waited for ata constant frequency. In the example of FIG. 6, the station 1 waits fora probe request at the frequency F3, and the station 2 waits for a proberequest at the frequency F1. However, the waiting frequency may beperiodically differing frequencies, and may be switched in the order ofF1→F2→F3→F1 . . . . , for example.

As described above, according to the present embodiment, by makingrandom the time during which a waiting state is continued, thefrequencies of the devices are not set to be different at all times, anda situation where the devices will not find each other can be prevented.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A wireless communication device comprising: amemory; and processing circuitry configured to: receive, during a listenstate, a probe request from a second device on a first frequency that isfixed in a first state of waiting on the fixed first frequency as asingle fixed channel of receiving the probe request; transmit, during asearch state, a probe request to the second device in a second state ofsending the probe request on plural channels of a fixed list offrequencies, the probe request being transmitted for each of the firstfrequency, a second frequency, and a third frequency switched in turn,the probe request also being transmitted after each occurrence of theswitching and within a single duration of the search state; cycle thefirst state and the second state; and randomize a period for which thefirst state is active while cycling, wherein the period is a length oftime that is an integer multiple of a time interval, the integermultiple being a randomly-generated number, wherein the periodrepresents a waiting cycle for the reception of the probe request, andthe waiting cycle associated with the first frequency is ended at atiming of elapse of the randomized period, and wherein in response toreceiving the probe request from the second device in the first state,the processing circuitry is configured to transmit a probe response tothe second device for the first frequency.
 2. The wireless communicationdevice according to claim 1, wherein the processing circuitry isconfigured to set a frequency channel of the wireless communicationdevice to the first frequency for a duration of receiving the proberequest.
 3. The wireless communication device according to claim 2,wherein the duration for receiving the probe request is a time periodduring which the processing circuitry switches to the first frequencyand waits for reception of the probe request from the second device. 4.The wireless communication device according to claim 1, wherein: theprocessing circuitry is further configured to randomize a period for thesecond state.
 5. The wireless communication device according to claim 1,wherein the probe request that is transmitted to the second deviceincludes identification information of the wireless communicationdevice.
 6. The wireless communication device according to claim 1,wherein the processing circuitry is further configured to insert FrameCheck Sequence in the probe request transmitted to the second device. 7.The wireless communication device according to claim 1, wherein theprobe request transmitted to the second device includes at least one ofan identifier of a network, a supported communication rate information,and a device name of the wireless communication device.
 8. The wirelesscommunication device according to claim 1, wherein a duration fortransmitting the probe request to the second device is a time periodduring which the wireless communication device is in the search stateand transmits one or more of the probe requests.
 9. A method ofcommunication implemented in a wireless communication device, the methodcomprising: receiving, during a listen state, a probe request from asecond device on a first frequency that is fixed in a first state ofwaiting on the fixed first frequency as a single fixed channel ofreceiving the probe request; transmitting, during a search state, aprobe request to the second device in a second state of sending theprobe request on plural channels of a fixed list of frequencies, theprobe request being transmitted for each of the first frequency, asecond frequency, and a third frequency switched in turn, the proberequest also being transmitted after each occurrence of the switchingand within a single duration of the search state; cycling the firststate and the second state; and randomizing a period for which the firststate is active while cycling, wherein the period is a length of timethat is an integer multiple of a time interval, the integer multiplebeing a randomly-generated number, wherein the period represents awaiting cycle for the reception of the probe request, and the waitingcycle associated with the first frequency is ended at a timing of elapseof the randomized period, and wherein in response to receiving the proberequest from the second device in the first state, further transmittinga probe response to the second device for the first frequency.
 10. Themethod according to claim 9, wherein a frequency channel of the wirelesscommunication device is set to the first frequency for a duration ofreceiving the probe request.
 11. The method according to claim 10,wherein the duration for receiving the probe request is a time periodduring which the wireless communication device switches to the firstfrequency and waits for reception of the probe request from the seconddevice.
 12. The method according to claim 9, further comprising:randomizing a period for the second state.
 13. The method according toclaim 9, wherein the probe request that is transmitted to the seconddevice includes identification information of the wireless communicationdevice.
 14. The method according to claim 9, further comprisinginserting a Frame Check Sequence in the probe request that istransmitted to the second device.
 15. The method according to claim 9,wherein the probe request that is transmitted to the second deviceincludes at least one of an identifier of a network, a supportedcommunication rate information, and a device name of the wirelesscommunication device.
 16. The method according to claim 9, wherein aduration for transmitting the probe request to the second device is atime period during which the wireless communication device is in thesearch state and transmits one or more of the probe requests.